89 research outputs found
Physics of a clumpy lensed galaxy at z=1.6
Observations have shown that massive star-forming clumps are present in the
internal structure of high-redshift galaxies. One way to study these clumps in
detail with a higher spatial resolution is by exploiting the power of strong
gravitational lensing which stretches images on the sky. In this work, we
present an analysis of the clumpy galaxy A68-HLS115 at , located
behind the cluster Abell 68, but strongly lensed by a cluster galaxy member.
Resolved observations with SINFONI/VLT in the near-infrared show Ha, Hb, [NII],
and [OIII] emission lines. Combined with images covering the B band to the
far-infrared and CO(2-1) observations, this makes this galaxy one of the only
sources for which such multi-band observations are available and for which it
is possible to study the properties of resolved star-forming clumps and to
perform a detailed analysis of the integrated properties, kinematics, and
metallicity. We obtain a stability of by
modeling the kinematics, which means that the galaxy is dominated by rotation,
but this ratio also indicates that the disk is marginally stable. We find a
high intrinsic velocity dispersion of km s that could be
explained by the high gas fraction of observed in this
galaxy. This high and the observed sSFR of
suggest that the disk turbulence and instabilities are mostly regulated by
incoming gas. The direct measure of the Toomre stability criterion of
could also indicate the presence of a quasi-stable thick disk.
Finally, we identify three clumps in the Ha map which have similar velocity
dispersions, metallicities, and seem to be embedded in the rotating disk. These
three clumps contribute together to on the SFR(Ha) of the galaxy and
show a SFR density about times higher than HII regions in the local
Universe.Comment: Accepted for publication in A&A. 10 pages, 7 figure
Probing the ISM Near Star Forming Regions with GRB Afterglow Spectroscopy: Gas, Metals, and Dust
We study the chemical abundances of the interstellar medium surrounding high
z gamma-ray bursts (GRBs) through analysis of the damped Lya systems (DLAs)
identified in afterglow spectra. These GRB-DLAs are characterized by large HI
column densities N(HI) and metallicities [M/H] spanning 1/100 to nearly solar,
with median [M/H]>-1. The majority of GRB-DLAs have [M/H] values exceeding the
cosmic mean metallicity of atomic gas at z>2, i.e. if anything, the GRB-DLAs
are biased to larger metallicity. We also observe (i) large [Zn/Fe] values
(>+0.6) and sub-solar Ti/Fe ratios which imply substantial differential
depletion, (ii) large a/Fe ratios suggesting nucleosynthetic enrichment by
massive stars, and (iii) low C^0/C^+ ratios (<10^{-4}). Quantitatively, the
observed depletion levels and C^0/C^+ ratios of the gas are not characteristic
of cold, dense HI clouds in the Galactic ISM. We argue that the GRB-DLAs
represent the ISM near the GRB but not gas directly local to the GRB (e.g. its
molecular cloud or circumstellar material). We compare these observations with
DLAs intervening background quasars (QSO-DLAs). The GRB-DLAs exhibit larger
N(HI) values, higher a/Fe and Zn/Fe ratios, and have higher metallicity than
the QSO-DLAs. We argue that the differences primarily result from
galactocentric radius-dependent differences in the ISM: GRB-DLAs preferentially
probe denser, more depleted, higher metallicity gaslocated in the inner few kpc
whereas QSO-DLAs are more likely to intersect the less dense, less enriched,
outer regions of the galaxy. Finally, we investigate whether dust obscuration
may exclude GRB-DLA sightlines from QSO-DLA samples; we find that the majority
of GRB-DLAs would be recovered which implies little observational bias against
large N(HI) systems.Comment: 16 pages, 9 figures. Submitted to Ap
Correlation analysis of vibration modes in physical vapour deposited Bi2Se3 thin films probed by the Raman mapping technique
In this work, the Raman spectroscopy mapping technique is used for the analysis of mechanical strain in Bi2Se3 thin films of various (3-400 nm) thicknesses synthesized by physical vapour deposition on amorphous quartz and single-layer graphene substrates. The evaluation of strain effects is based on the correlation analysis of in-plane (E2g) and out-of-plane (A21g) Raman mode positions. For Bi2Se3 films deposited on quartz, experimental datapoints are scattered along the line with a slope of similar to 0.85, related to the distribution of hydrostatic strain. In contrast to quartz/Bi2Se3 samples, for graphene/Bi2Se3 heterostructures with the same thicknesses, an additional negative slope of similar to-0.85, which can be associated with the distribution of the in-plane (a-b) biaxial tensile strain due to the film-substrate lattice mismatch, is observed. The algorithm of phonon deformation potential (PDP) calculation based on the proposed strain analysis for the 3 nm thick Bi2Se3 film deposited on the graphene substrate, where the strain is considered to be coherent across the thickness, is demonstrated. The PDPs for biaxial in-plane strain of the Bi2Se3 3 nm film in in-plane and out-of-plane modes are equal to -7.64 cm(-1)/% and -6.97 cm(-1)/%, respectively
ALMA observations of a metal-rich damped Ly{\alpha} absorber at z = 2.5832: evidence for strong galactic winds in a galaxy group
We report on the results of a search for CO(3-2) emission from the galaxy
counterpart of a high-metallicity Damped Ly-alpha Absorber (DLA) at z=2.5832
towards the quasar Q0918+1636. We do not detect CO emission from the previously
identified DLA galaxy counterpart. The limit we infer on M_gas / M_star is in
the low end of the range found for DLA galaxies, but is still consistent with
what is found for other star-forming galaxies at similar redshifts. Instead we
detect CO(3-2) emission from another intensely star-forming galaxy at an impact
parameter of 117 kpc from the line-of-sight to the quasar and 131 km s^-1
redshifted relative to the velocity centroid of the DLA in the quasar spectrum.
In the velocity profile of the low- and high-ionisation absorption lines of the
DLA there is an absorption component consistent with the redshift of this
CO-emitting galaxy. It is plausible that this component is physically
associated with a strong outflow in the plane of the sky from the CO-emitting
galaxy. If true, this would be further evidence, in addition to what is already
known from studies of Lyman-break galaxies, that galactic outflows can be
traced beyond 100 kpc from star-forming galaxies. The case of this z=2.583
structure is an illustration of this in a group environment.Comment: 7 pages, 5 figures, accepted for publication in MNRA
On the Incidence of Strong MgII Absorbers Along GRB Sightlines
We report on a survey for strong (rest equivalent width W_r >= 1A),
intervening MgII systems along the sightlines to long-duration gamma-ray bursts
(GRBs). The GRB spectra which comprise the survey have a heterogeneous mix of
resolution and wavelength coverage, but we implement a strict, uniform set of
search criteria to derive a well-defined statistical sample. We identify 15
strong MgII absorbers along 14 GRB sightlines (nearly every sightline exhibits
at least one absorber) with spectra covering a total pathlength Delta z = 15.5
at a mean redshift = 1.1. In contrast, the predicted incidence of such
absorber systems along the same path length to quasar sightlines is only 3.8.
The roughly four times higher incidence along GRB sightlines is inconsistent
with a statistical fluctuation at greater than 99.9% c.l. Several effects could
explain the result: (i) dust within the MgII absorbers obscures faint quasars
giving a lower observed incidence along quasar sightlines; (ii) the gas is
intrinsic to the GRB event; (iii) the GRB are gravitationally lensed by these
absorbers. We present strong arguments against the first two effects and also
consider lensing to be an unlikely explanation. The results suggest that at
least one of our fundamental beliefs on absorption line research is flawed.Comment: 5 pages, 3 figures. Submitted to ApJ
The KMOS Lens-Amplified Spectroscopic Survey (KLASS): Kinematics and clumpiness of low-mass galaxies at cosmic noon
We present results from the KMOS Lens-Amplified Spectroscopic Survey (KLASS),
an ESO Very Large Telescope (VLT) large program using gravitational lensing to
study the spatially resolved kinematics of 44 star-forming galaxies at
0.6<z<2.3 with a stellar mass of 8.1<log(M/M)<11.0. These
galaxies are located behind six galaxy clusters selected from the HST Grism
Lens-Amplified Survey from Space (GLASS). We find that the majority of the
galaxies show a rotating disk, but most of the rotation-dominated galaxies only
have a low ratio (median of
). We explore the Tully-Fisher relation by
adopting the circular velocity,
, to account for pressure
support. We find that our sample follows a Tully-Fisher relation with a
positive zero-point offset of +0.18 dex compared to the local relation,
consistent with more gas-rich galaxies that still have to convert most of their
gas into stars. We find a strong correlation between the velocity dispersion
and stellar mass in the KLASS sample. When combining our data to other surveys
from the literature, we also see an increase of the velocity dispersion with
stellar mass at all redshift. We obtain an increase of
with stellar mass at 0.5<z<1.0. This could indicate
that massive galaxies settle into regular rotating disks before the low-mass
galaxies. For higher redshift (z>1), we find a weak increase or flat trend. We
investigate the relation between the rest-frame UV clumpiness of galaxies and
their global kinematic properties. We find no clear trend between the
clumpiness and the velocity dispersion and . This
could suggest that the kinematic properties of galaxies evolve after the clumps
formed in the galaxy disk or that the clumps can form in different physical
conditions.Comment: 19 pages, 9 figures. Accepted for publication in MNRA
Chemical diversity of gas in distant galaxies: The metal and dust enrichment and variations within absorbing galaxies
The chemical composition of gas in galaxies can be measured in detail from
absorption spectroscopy. By studying gas in galaxies in this way, it is
possible to investigate the small and faint galaxies, which are the most
numerous in the universe. In particular, the chemical distribution of gas in
absorbing systems gives us insight into cycles of gas in and around galaxies.
Here we study chemical enrichment within 64 Damped Lyman-alpha Absorption (DLA)
systems between . We use high-resolution spectra from VLT/UVES
to infer dust depletion from relative abundances of several metals. We perform
a component-by-component analysis within DLAs, and characterise variations in
their chemical enrichment. Unlike hydrogen, the metal columns can be
characterised for individual components. We use them to derive the dust
depletion ([Zn/Fe]fit), as an indicator for chemical enrichment. We find that
some DLAs are chemically diverse within themselves, with [Zn/Fe]fit ranging up
to 0.62 dex within a single system. This suggests that absorbing gas within
these galaxies is chemically diverse. Although we do not find a clear trend of
decreasing dust depletion with redshift, we do see that the most chemically
enriched systems are at lower redshifts. We also observe evidence for dust-poor
components at all redshifts, which may be due to the accretion of pristine gas
onto galaxies. We combine the chemical and kinematic properties of the
individual gas components and observe potential signatures of infalling gas,
with low depletion at velocities below 100km/s, and outflows, with high
depletion and velocities of 600km/s. We find over-abundances of
alpha-elements (an enhancement of 0.3dex) and under-abundances of Mn in
several components, which is likely a signature of core-collapse SNe
nucleosythesis in the ISM. We observe these effects mostly at lower levels of
chemical enrichment.Comment: 56 pages, 99 figures, Accepted for publication in A&A, Abstract
abridged for arXi
Gas Accretion Traced in Absorption in Galaxy Spectroscopy
The positive velocity shift of absorption transitions tracing diffuse
material observed in a galaxy spectrum is an unambiguous signature of gas flow
toward the host system. Spectroscopy probing, e.g., NaI D resonance lines in
the rest-frame optical or MgII and FeII in the near-ultraviolet is in principle
sensitive to the infall of cool material at temperatures ~ 100-10,000 K
anywhere along the line of sight to a galaxy's stellar component. However,
secure detections of this redshifted absorption signature have proved
challenging to obtain due to the ubiquity of cool gas outflows giving rise to
blueshifted absorption along the same sightlines. In this chapter, we review
the bona fide detections of this phenomenon. Analysis of NaI D line profiles
has revealed numerous instances of redshifted absorption observed toward
early-type and/or AGN-host galaxies, while spectroscopy of MgII and FeII has
provided evidence for ongoing gas accretion onto >5% of luminous, star-forming
galaxies at z ~ 0.5-1. We then discuss the potentially ground-breaking benefits
of future efforts to improve the spectral resolution of such studies, and to
leverage spatially-resolved spectroscopy for new constraints on inflowing gas
morphology.Comment: 21 pages, 7 figures. Invited review to appear in Gas Accretion onto
Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e,
to be published by Springe
Big Bang Nucleosynthesis and Particle Dark Matter
We review how our current understanding of the light element synthesis during
the Big Bang Nucleosynthesis era may help shed light on the identity of
particle dark matter.Comment: a mini-review for the NJP special issue on dark matte
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